A109288 Semiprimes equal to p*q + 1, where p and q are distinct primes.

15, 22, 34, 35, 39, 58, 86, 87, 94, 95, 119, 123, 134, 142, 143, 146, 159, 178, 202, 203, 206, 214, 215, 218, 219, 254, 299, 302, 303, 327, 335, 382, 394, 395, 446, 447, 454, 482, 502, 515, 527, 538, 543, 554, 566, 623, 634, 635, 695, 698, 699, 707, 718, 746

Offset: 1

Author

Giovanni Teofilatto, Aug 20 2005

Keywords

• nonn

Links

• Amiram Eldar, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A109287, A109289, A109290, A263990.

Programs

Mathematica

With[{nn=60},Take[Select[Union[Times@@#+1&/@Subsets[Prime[Range[2nn]],{2}]],PrimeOmega[#]==2&],nn]] (* Harvey P. Dale, Apr 28 2018 *)
Select[Range[1000], !IntegerQ[Sqrt[#-1]] && PrimeOmega[#] == PrimeOmega[#-1] == 2 &] (* Amiram Eldar, Aug 08 2025 *)

PARI

for(i=1,1000,if(bigomega(i)==2&&bigomega(i+1)==2&&issquare(i)==0,print1(i+1,","))) \\ Lambert Klasen (lambert.klasen(AT)gmx.net), Aug 21 2005

Formula

a(n) = A263990(n) + 1. - Amiram Eldar, Aug 08 2025

Extensions

More terms from Lambert Klasen (lambert.klasen(AT)gmx.net), Aug 21 2005